Various medication injection pen devices are known in the prior art. These prior art devices sometimes include features for enabling a user to correct a dose that has been set too large, which may be referred to as “dial back”. Another feature that may be provided by some of the prior art devices is the ability to control a last dose of a medication cartridge such that a user cannot set a dose greater than the remaining amount of medication in the cartridge. This feature is sometimes referred to as last dose control or last dose management. Both of these features are desired by users of such pen devices; however, the prior art devices do not satisfactorily meet these needs. Many prior art devices may provide one of these features, but not both. Further, many of the prior art devices require additional steps for performing dial back, which are cumbersome and not intuitive to the user. Thus, there is a need in the art to provide improved functionality of dial back and last dose control mechanisms together in a medication injection pen.
Prior art pen injection devices commonly use driving components that are snap fit together to secure the components in place, thereby requiring tight manufacturing tolerances. Additionally, many prior art pen injection devices utilize one-way ratchet systems that are difficult for a user to access for customization. Such ratchet systems typically require a substantial and complex manufacturing process to accomplish. Accordingly, a need exists for a pen injection device that eliminates snap fitting components together to provide a simple assembly that is easily customizable.